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CMSI 284 Computer System Organization/Systems Programming, Spring 2019

Assignment 0404

Our second C set is not strictly harder, but does use some slightly more sophisticated techniques such as memory allocation and multiple files.

Background Reading

Pretty much all of the information you need can be found in Dr. Toal’s Introduction to C page, as well as many other C programming sites on the web.

You will also want to reference the reverse-range-in-place sample to see how multiple files would be named and organized, including test programs. (do note though that one of the files—indicated in the comments—is provided purely for information purposes and is actually an example of how not to include one file in another)

For Submission: From C to Shining C

Write the requested C programs. Note that for these programs, part of the exercise is to write them using a particular structure. Even though these programs can also be written in single monolithic files, precisely knowing how to not write them that way is part of the point of the assignment.

Madlib

Implement a madlib function in its own file, madlib.c, with this signature:

char* madlib(char* template, char* adjective, char* noun, char* verb);

template should be a C format string with three %s placeholders, one each for the given adjective, noun, and verb strings. madlib should create a new string consisting of the template with its %s placeholders replaced by the three words (cough sprintf cough). For example,

madlib("The %s %s likes to %s in the moonlight", "brilliant", "git", "swim")

…should evaluate to The brilliant git likes to swim in the moonlight.

Accompany your function file with a test harness, madlib-test.c, that uses the C assert function to show that your madlib function works properly.

Madlib-by-Numbers

Implement an ordered madlib function in its own file, madlib-by-numbers.c, with this signature:

char* madlib_by_numbers(char* template, int word_count, char* words[]);

For this variation of the function, template should be a C format string where single digits 0 to 9 may be substituted by the corresponding word in the given words array. If a digit exceeds the maximum index in the words array (as indicated by the word_count parameter), no substitution takes place. As with madlib, a new string should be created. For example, given the string array char* words_to_use[] = { "swim", "brilliant", "git" }, the expression

madlib_by_numbers("The 1 2 likes to 0 in the 1 moonlight", 3, words_to_use)

…should evaluate to The brilliant git likes to swim in the brilliant moonlight.

Note that madlib_by_numbers can do the following:

  • Use a word multiple times: The same “word number” can appear in the template string more than once
  • Substitute words in any order: Larger “word numbers” can appear before smaller ones

On the other hand, madlib_by_numbers can not do the following:

  • Substitute a double-digit index: e.g., 12 in the template string substitutes words 1 and 2, not word 12; if this appeared in the template string above, the substitution will be brilliantgit
  • As such, it thus follows that madlib_by_numbers will not handle word lists of more than 10 elements: words 10 and above will simply have no place to go

To prevent potential vulnerabilities (can you see why?), word_count should not accept values greater than 10. A word_count of 10 or greater should return an empty string.

Accompany your file with a test harness, madlib-by-numbers-test.c, that uses the C assert function to show that your madlib_by_numbers function works properly.

Protip: Strongly consider defining additional functions in madlib-by-numbers.c that perform intermediate computations for you. This not only decreases the complexity of your individual functions, but provides additional units of functionality that you can test separately.

Reverse Words

Use the sample reverse_range_in_place function to implement:

void reverse_words(char* string);

This function does what you think it does: it reverses the words, in place, within the given string (i.e., a new string is not created; instead, the original string is modified into its reversed-words version). Note that modern languages generally don’t allow in-place string modification, opting to create new strings instead. With C, however, this remains possible.

To keep things simple, we will define a “word” as any sequence of non-space characters, including punctuation, numbers, etc. For example, if the string argument pointed to Hello, my friends!, reverse_words should change its contents into friends! my Hello,.

You may not allocate additional memory, and the only other string function that you may use is strlen. Watch out for edge cases such as leading/trailing spaces, multiple spaces in between words, etc. Big implementation clue: There is no need to particularly preserve multiple-space gaps. If those shift around in the resulting string, that’s OK.

Organize your source code as follows: place your function in reverse-words.c with an accompanying header file reverse-words.h (just like the included sample and starter code). Supply a test harness to demonstrate that your function works as specified; call this reverse-words-test.c. The original reverse_range_in_place code should not be modified, and used as provided.

How to Turn it In

Commit the requested source code (and just the source code)—header files, implementation files, and test files—to this repository. To avoid filename confusion, stubs for the requested files are already part of the repository. The reverse_range_in_place implementation has also been copied over from the GitHub bazaar.

Specific Point Allocations

This assignment is scored according to outcomes 2a, 2b, and 4a to 4f in the syllabus. For this particular assignment, graded categories are as follows:

Category Points Outcomes
Madlib 30 points total
• Compiles and runs without unexpected errors 5 points 4a, 4d
• Correct functionality 20 points 2a, 2b, 4a, 4d
• Adequate test cases 5 points 2a, 2b, 4a, 4d
Madlib-by-Numbers 35 points total
• Compiles and runs without unexpected errors 5 points 4a, 4d
• Correct functionality 20 points 2a, 2b, 4a, 4d
• Adequate test cases 10 points 2a, 2b, 4a, 4d
Reverse Words 35 points total
• Compiles and runs without unexpected errors 5 points 4a, 4d
• Correct functionality 20 points 2a, 2b, 4a, 4d
• Adequate test cases 10 points 2a, 2b, 4a, 4d
Missing test program deduction only 4a, 4b
Hard-to-maintain or error-prone code deduction only 4b
Non-compliant file structure deduction only 4b
Hard-to-read code deduction only 4c
Version control deduction only 4e
Punctuality deduction only 4f
Total 100

Note that inability to compile and run to begin with will negatively affect correct functionality and the adequacy of test cases (because this will cast doubt on whether the tests work).

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